Pressure equalizing elements assist in the ventilation of tightly closed housings, particularly of electrical circuit devices, as they are used in motor vehicles. Such elements minimize the seeping of water into the housing interior, but permit compensation of pressure differences, for example arising from temperature changes, between the interior air and the surrounding environment. Pressure equalization is, however, only assured if water reaching the pressure equalization element can immediately run off.
German patent disclosure DE-OS 37 07 050 of March 5, 1987, published Sept. 15, 1988, HESS & HOFMEISTER, discloses using, as a pressure compensating element, a flat membrane of air-transmitting material, for example, a polytetrafluoroethylene (PTFE) foil material. This membrane permits compensation of pressure differences between the two sides of the membrane.
The disadvantage of this pressure equalizing element is that the pressure equalization is not possible if water is standing on the membrane. This means that such an element can only be located in the housing wall of such an electrical device, in order that water reaching the membrane will run off.